This invention relates to manholes formed of cast-concrete walls and, more particularly, to an apparatus which can be used to form holes to accommodate sewer pipe in the wall of such a manhole.
It has been found that manholes can most expeditiously be formed by drilling a hole in the ground, placing at least one cylindrical form within the hole and pouring concrete between the form and the wall of the hole. A manhole formed in such a manner is described in U.S. Pat. No. 4,127,990, the subject matter of which was invented by the same individual who is the inventor of the present invention. The subject matter of that patent is incorporated herein as though fully set forth.
In the embodiment of the invention which is the subject of that patent shown in FIGS. 5 and 6 and discussed in col. 4, lns. 54-69 and col. 5, lns. 1-47, a manhole is formed prior to the laying of sewer pipe by excavating a hole and positioning an outer form in the hole. An inner form is positioned concentric with the outer form with its lower end higher than the lower end of the outer form and concrete is poured to form a base between the ends of the forms. Alternatively, the base can be formed before the inner form is moved into place.
When the two forms are appropriately positioned after the base is poured, small quantities of sand are placed above the base and between the two forms generally in locations where sewer pipes will be connected to the manhole. Concrete is then poured between the forms. After the concrete cures and the forms are removed as described in the patent the sand either falls away or can easily be removed and small openings in the wall where the sand was positioned during the pouring of the concrete are then manually enlarged with a chisel or the like for providing holes through which sewer pipe can communicate with the inner cavity of the manhole.
This method of forming sewer pipe holes is time consuming and expensive. Although other types of non-reusable concrete blockouts have been used, no suitable apparatus is known which can effectively be used as part of the form which has the capability of being reused.